The proposal is a competing continuation of a subproject in an earlier program project grant (P01 NS32386). The studies aim at continuing the examination of the role of the human somatosensory thalamus (Vc) in pain. The long-term objective is to define the role of thalamic activity in signaling thermal sensations and pain sensations using a combination of neurophysiological and psychophysical techniques. Single unit recordings in Vc are performed in chronic pain patients and patients with movement disorders. Recordings in the latter group are considered as generating control data. Aim 1 examines the properties of spike trains in Vc to painful and nonpainful mechanical and thermal stimuli, in movement disorder patients. They also plan on testing whether the spike train properties change with changes in stimulus intensity and as a function of attention. Aim 2 examines the sensations evoked by electrical stimulation within Vc in movement disorder patients. They will examine the sensations as a function of temporal properties of stimuli in an effort to distinguish between paresthesias, warm, cool, & pain perceptions, and to determine the relationship between temporal patterns and intensity perception, as well as relate the stimulus pattern to the characteristics of the neuronal discharge with the equivalent sensation. Aim 3 examines the same questions as in aims 1 & 2 in the Vc of chronic pain patients to differentiate changes in coding properties between the two groups of subjects.